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AD421BN Fiches technique(PDF) 1 Page - Analog Devices |
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AD421BN Fiches technique(HTML) 1 Page - Analog Devices |
1 / 14 page FUNCTIONAL BLOCK DIAGRAM LOCAL OSCILLATOR SWITCHED CURRENT SOURCES AND FILTERING BANDGAP REFERENCE REF IN (+2.5V) REF OUT1 (+1.25V) REF OUT2 (+2.5V) LV VCC DRIVE COMP BOOST LOOP RTN C1 C2 C3 COM LATCH CLOCK DATA 40 16-BIT SIGMA- DELTA DAC 75k 112.5k 134k 121k 80k AD421 INPUT SHIFT REGISTER DAC LATCH POWER-ON RESET REV. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a FEATURES 4 mA to 20 mA Current Output HART® Compatible 16-Bit Resolution and Monotonicity 0.01% Integral Nonlinearity 5 V or 3 V Regulator Output 2.5 V and 1.25 V Precision Reference 750 A Quiescent Current max Programmable Alarm Current Capability Flexible High Speed Serial Interface 16-Lead SOIC and PDIP Packages Loop-Powered 4 mA to 20 mA DAC AD421 PRODUCT HIGHLIGHTS 1. The AD421 is a single chip, high performance, low cost solution for generating 4 mA to 20 mA signals for smart industrial control transmitters. 2. The AD421’s regulated supply voltage can be used to power any additional circuits in the transmitter. The regulated output value is pin selectable as either +3 V, +3.3 V or +5 V. 3. The AD421’s on-chip references can provide a precision reference voltage to other devices in the system. This refer- ence voltage can be either +1.25 V or +2.5 V. 4. The AD421 is fully compatible with standard HART cir- cuitry or other similar FSK protocols. 5. With the addition of a single discrete transistor, the AD421 can be operated from VCC + 2 V min to a maximum of the breakdown voltage of the pass transistor. 6. The AD421 converts the digital data to current with 16-bit resolution and monotonicity. Full-scale settling time to ±0.1% typically occurs within 8 ms. 7. The AD421 features a programmable alarm current capabil- ity that allows the transmitter to send out of range currents to indicate a transducer fault. HART is a registered trademark of the HART Communication Foundation. GENERAL DESCRIPTION The AD421 is a complete, loop-powered, digital to 4 mA to 20 mA converter, designed to meet the needs of smart trans- mitter manufacturers in the Industrial Control industry. It pro- vides a high precision, fully integrated, low cost solution in a compact 16-lead package. The AD421 is ideal for extending the resolution of smart 4 mA to 20 mA transmitters at very low cost. The AD421 includes a selectable regulator that is used to power itself and other devices in the transmitter. This regulator pro- vides either a +5 V, +3.3 V or +3 V regulated output voltage. The part also contains +1.25 V and +2.5 V precision references. The AD421 thus eliminates the need for a discrete regulator and voltage reference. The only external components required are a number of passive components and a pass transistor to span large loop voltages. The AD421 can be used with standard HART FSK protocol communication circuitry without any degradation in specified performance. The high speed serial interface is capable of oper- ating at 10 Mbps and allows for simple connection to com- monly-used microprocessors and microcontrollers via a standard three-wire serial interface. The sigma-delta architecture of the DAC guarantees 16-bit monotonicity while the integral nonlinearity for the AD421 is ±0.01%. The part provides a zero scale 4 mA output current with ±0.1% offset error and a 20 mA full-scale output current with ±0.2% gain error. The AD421 is available in a 16-lead, 0.3 inch-wide, plastic DIP and in a 16-lead, 0.3 inch-wide, SOIC package. The part is speci- fied over the industrial temperature range of –40 °C to +85°C. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2000 |
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